The overall aim of this multdisciplinary cooperative study is to provide prospective definitions of renovascular hypertension, as well as an objective basis for the diagnosis and treatment of this condition. In this study, of 2,442 patients, 1,128 were judged to have primary (essential) hypertersion, 880 renovascular disease, 355 parenchyma kidney disease and 79 miscellaneous disorders. There wee 577 renovascular operative procedures and 502 patients with renal arterial disease. It is proposed to analyze these data with the following objectives: 1) to define the natural history of renovascular hypertesion, stratified by etiology, age, race and sex, 2) to determine the clinical characteristics of renovascular hypertension as compared with primary (essential) hypertension, 3) to compare the diagnostic and prognostic accuracy and the morbidity of the renal arteriogram, the radio-isotope renogram, the intravenous urogram, individual kidney function tests, renal biopsies, pressure gradients across stenotic lesions of the renal arteries. To define quantitative criteria for the interpretation of each of these tests singly and in clusters. To maximally discriminate essential hypertension from renovascular hypertension on the basis of retrospective statistical analyses. 4) To evaluate the short and long term effects of renal artery constructive surgery and nephrectomy; the morbidity and mortality of various types of surgery; to determine the indications for surgical treatment of renovascular hypertension and the preferable surgical procedure for each type of anatomic lesion, 5) to delineate the characteristics of a large number of patients with unequivocal primary (essential) hypertension.